December is the month when the Washington area's winter begins to look real. Most trees are bare-branched, or have only crinkly, dead leaves clinging to them. Garden colors are back to basic brown. The air, buzzing with insects in summer, is cold and still.
Why, then, does witch hazel bloom in chilly weather, when so little else does? Why do pansies flower red, yellow and purple, even amid snow? Why does the sweet-smelling Japanese apricot blossom in December?
Why do they stick their necks out when most plants are crouched low? The answer is that there is opportunity in being an exception.
"The way I think of it is filling a niche," said horticulturist Scott Aker of the National Arboretum. "When you think about flowering in particular, it's an expensive process for a plant. It's putting a lot of energy into making progeny. If you're a plant inclined to bloom at the height of spring, flowers are cheap in April and May. And there are a lot of pollinators out there.
"Some of the things that bloom at these odd times do so because there's a much greater chance of being pollinated," he said. "You're the only plant on the block."
There are not many insects out and about during the winter, but apparently there are enough to do the job. Bees come out of their hives when the temperature hits 50 or so. By late January, Aker said, they "are running out of honey and frantically trying to collect whatever food they can."
"A lot of the native bees come out in the early winter," said Brenda Skarphol, curatorial horticulturist at Fairfax County's Green Spring Gardens Park.
"You'll see ants sometimes. Even little flies. There are pollinators that don't need very warm temperatures at all."
Aker has a saying to help you determine which species pollinates a plant that blooms in winter (or any other time): "Just as sweet flowers attract bees, stinky flowers attract flies."
Winter is dangerous for plants because freezing temperatures transform the moisture in the plant's cells into ice crystals that rupture their membranes. Evergreens are able to resist this by being tough: Their foliage is coated with wax and their cell fluid contains an anti-freeze. Most other perennials protect themselves by dropping their thin-skinned, easily frozen leaves. But some are able to flower through the winter by being built to withstand the chill or by being able to rein themselves in when it gets cold.
Pansies and other winter-hardy plants are able to push water out of their cells if temperatures plunge, relocating it to their roots underground where it is warmer. Witch hazel can unfurl its blooms when it is particularly warm and it wants to attract pollinators. When it is cold or rainy, its blooms curl up to reduce exposure.
In addition to regular winter-flowering trees, there are some spring-flowering trees that burst into bloom when a stray warm spell interrupts chilly weather. People worry about these trees, but horticulturists say the winter blooming won't kill them or stifle their blossoms in the spring.
Spring-blooming trees need a certain number of chilling hours before their buds come out, said Phil Normandy, plant collections manager at Brookside Gardens in Montgomery County, but some do not need much, and by January or February they may have met their quota. A series of winter days in the 50s and 60s will be enough for them to break bud, he said.
Or there may be a cherry tree planted in a sheltered urban courtyard, surrounded by stone walls that hold the sun's warmth and keep the temperature at 70 when it reads 50 degrees on the official airport thermometer. When that tree flowers in January, Aker said, it is not blooming at the wrong time.
An early winter bloom might reduce the show a bit in the spring, but Normandy said trees usually have plenty of blossoms left over.
"Some plants bloom sporadically," he said. "They are okay."
-- D'Vera Cohn